Industry has long recognized the advantages of storing fuel and other fluids underground. Storage underground has known advantages such as moderating thermal fluctuations of stored fuel owing to the surrounding earth serving as a heat sink, as well as maintaining open space above ground for other uses. For example, in a typical gasoline station, different grades of gasoline and diesel fuel are stored in underground tanks for distribution to above ground fuel pumps by an underground fluid piping system.
It has been recognized, however, that the underground storage of fluids is not problem-free. Leakage of hazardous fluids from tanks and pipelines is believed to cause environmental problems such as ground water contamination. Existing, aged, underground fluid distribution systems, many of which contain metal components, have been leaking not only at the many connector joints in the piping system, but have also been found to "rust out" and leak fluids into the ground.
Society is demanding elimination of the leaking of fluids, such as diesel fuel and gasoline from service stations, that harm the environment.
Furthermore, federal regulations will soon require that underground fuel distribution systems over a certain age be replaced.
U.S. Pat. No. 5,058,633 to Sharp discloses a spill containment assembly for the fill pipe of an underground storage tank. The Sharp device has a secondary containment chamber for containing any leakage through the fill pipes. The secondary containment chamber includes a corrugated sidewall portion capable of limited expansion and contraction to allow a degree of tolerance in the distance between the underground storage tank's top surface and a level ground surface cover for the chamber. The expansion capability allows the assembly to withstand a certain degree of ground movement such as comes from freeze/thaw situations without a cracking problem. Although the Sharp system undoubtedly works, any movement, however slight, may eventually lead to fatigue and cracking.
U.S. Pat. No. 5,040,408 to Webb discloses a secondary containment system using flexible piping that includes a hollow riser extension having scorelines, typically spaced inch apart, serving as cutting guide lines for height sizing. However, Webb discloses no use for such scorelines other than changing the height of the riser extension.